1. Field of the Invention
The present invention relates to a control system for a clothes dryer and, more particularly, to a clothes dryer control system incorporating a moisture sensor used to terminate a drying process when the amount of moisture present in the clothes inside the dryer reaches a desired level as selected by a user.
2. Discussion of the Prior Art
It is well known in the art to provide a clothes dryer with a simple time-dry control, in addition to a sensor-dry mode. When the time-dry control is used, the user simply places wet articles inside the dryer and selects the duration for the drying process. Because there is little or no automatic control or adjustment during the process, the drying process simply continues until the time expires. The result can be inefficient, because it is difficult for a user to accurately estimate the time required to reach a desired, final moisture level prior to operating the machine.
In comparison, sensor-dry modes are provided to automatically control a drying operation. Specifically, when a sensor-dry mode is selected, the user places wet articles inside the dryer drum and selects a desired final dryness level. Instead of forcing the user to guess as to how long the process should take, the machine stops when the desired dryness level is reached. For this purpose, the machine includes at least one moisture sensor for detecting the level of moisture of the articles. The machine simply operates until the moisture sensor detects the final desired dryness level selected by the user. By terminating the process upon achieving the desired final dryness level, there is no need to re-start the process to finish incomplete drying. In addition, extra energy is not expended to dry the articles beyond the desired dryness level.
Electronic controls have been developed to assist in the operation of such an automatic drying processes. For example, U.S. Pat. No. 3,762,064, to Offut, discloses a system for automatic operation of a dryer in which extra time is added to a drying process according to a predetermined table. A selection of a dryness level beyond a predetermined level (e.g. damp-dry) results in the addition of extra time. The duration of this extra time is dependent upon the length of time required to reach the predetermined dryness level and the desired final dryness level selected by the user. While this system incorporates a moisture sensor for making a drying operation more efficient, this system is nevertheless highly inefficient, because only one threshold dryness level is detected and the final dryness level is never actually measured, as the time to reach that level is simply estimated. Therefore, just as in time dry modes, the articles will often either be under-dried and still wet, or over-dried.
U.S. Pat. No. 4,477,892, to Cotton, represents an improvement over the system disclosed in the ""064 patent and includes sensors or electrodes which contact the wet articles to determine the current moisture level contained therein. Through the system of this patent, the current moisture level inside the machine can be measured at a variety of continuous levels. By comparing the number of conductive electrode xe2x80x9chitsxe2x80x9d during a given time period, it is possible to estimate the current degree of dryness.
However, there still remains a concern regarding the programming of the operation controller. U.S. Pat. No. 6,020,698 to Stenger et al. discloses the use of multiple binary switches to program an electromechanical timer and an electronic control circuit. A plurality of timer switches are included in relation to a control knob to provide control input, and changing from one control position to an adjacent control position results in a switch either being opened or closed. However, this system only allows a small number of different settings to the microprocessor or electronic control circuit, dependent upon the number of timer switches. Increasing the variability, therefore, requires increasing the number of timer switches and, accordingly, greatly increasing the cost.
Based on the above, there exists a need in the art to provide a control system for a clothes dryer which allows for programming of a wide range of final desired dryness levels, while efficiently drying the clothes contained therein, in a cost efficient manner. Additionally, there exists a need for a clothes dryer which quickly recognizes a dry condition upon commencing a drying cycle and powers down without running a heater.
The present invention is particularly directed to a control system for a clothes dryer including a timer used to calculate an initial position of a dial or control knob. For instance, during operation of the control system of the invention, the user can select a sensor-dry mode by rotating the dial to a position indicating the final desired dryness level of the articles contained within the dryer. Upon pressing a start button, an internal motor quickly rotates the dial to a preset position, and the time to do so is measured. Because the control system of the invention is programmed with the speed at which the dial is rotated, the initial position of the knob can be quickly and easily determined by multiplying the rotational speed by the time required to rotate the knob. The result is compared to the output from a typical moisture sensor, and drying operation is halted when the detected moisture level reaches the selected level.
Preferably, the control system, via the motor, is capable of driving the dial at different speeds. The first, or fast speed, is used during the initial programming procedure, as described above. A second, or slower speed, is used during the remainder of the sense dry cycle. By providing these varying rotational speeds, greater control and variability is permitted.
Additional objects, features and advantages of the invention will become more readily apparent from the following detailed description of a preferred embodiment thereof, when taken in conjunction with the drawings wherein like reference numerals refer to corresponding parts in the several views.